The present invention relates to a gas delivery apparatus for administering a gas to a patient during surgery, and more particularly for delivering anesthetic to a patient during surgery.
During surgical procedures, there is a need to anesthetize a patient in order to eliminate, or at least reduce: pain associated with the procedure; and movement of the patient during the procedure. Anesthesia is considered a drug-induced depression of at least a portion of nervous system, or portion thereof, of the patient.
In the sequence of events of drug-induced depression of the central nervous system, there occurs a level of depression that allows the muscles of the pharynx (e.g. the tongue) to relax causing soft-tissue structures to collapse into and obstruct the airway. This happens at an earlier stage than that at which the muscles of respiration (e.g. the diaphragm) cease to function. In other words, a condition known as “obstructive apnea,” where the diaphragm is struggling to pull air through an obstruction of the upper airway occurs before the diaphragm itself ceases to function (“central apnea”). In this sequential depression of the central nervous system, death occurs from Asphyxia before the drug itself can produce complete depression of the nervous system.
Similarly, even partial obstruction will cause disastrous consequences of an immediate and/or long-term nature. For example the resulting hypoxia (i.e., oxygen deficiency) will cause a reflex constriction of blood vessels in the lungs leading to pulmonary hypertension and the right portion of the heart's failure to pump blood efficiently through the lungs to the left portion of the heart. Accordingly, the heart is unduly taxed and the circulatory reserves of well oxygenated blood are impaired. The resulting hypercarbia (i.e., the abnormal accumulation of carbon dioxide) will cause acidosis (i.e., the accumulation of acid) leading to depression of organ systems. The central nervous system, for instance, will become progressively depressed to a deep coma directly related to the level of retained carbon dioxide. Further, the resulting stronger negative intra-thoracic pressure, that is generated by the bellows action of the diaphragm pulling on the chest cavity as the patient attempts to draw air through an obstructed upper airway, leads to two problems. First, a greater negative intra-pulmonary pressure (i.e., the negative pressure transmitted to inside the lungs) dilates small blood vessels to cause excessive blood flow around the alveoli (i.e., the small air sacs). Concurrently, a vacuum is created which sucks fluid out of the circulation to fill the void generated within the alveoli. Hypoxia ensues, first, from the mismatch of circulation to ventilation and, then, rapidly deteriorates as pulmonary edema (i.e., fluid in the air sacs) worsens. Second, a greater negative pressure in the chest cavity is also transmitted to the esophagus. An esophageal pressure more negative, relative to the pressure within the stomach, establishes a pressure gradient which favors the reflux of gastric acid up the esophagus where it will bum pharyngeal structures and, if aspirated into the lungs, will cause severe and, sometimes, fatal destruction of lung tissue.
An upper airway obstruction occurs upon the induction of almost every general anesthetic and is a frequent occurrence during the administration of heavy sedation for procedures done nominally under “local anesthesia with sedation.” Under most conditions, the treatment is so routine as to be taken for granted by practitioners skilled in airway management.
The condition which has been called SNOR (Syndrome of Narcogenic Obstructive Respiration) is a common occurrence in the practice of anesthesia. Drugs, which induce depression of the central nervous system to prevent the perception of pain, concurrently induce upper airway obstruction. Many airway devices and methods are used to alleviate the problem. One method, not yet widely practiced, involves the delivery of air and/or oxygen and anesthetic gases under positive pressure through the nose of the patient to prevent airway obstruction in a fashion very similar to that used in the home therapy of Obstructive Sleep Apnea (OSA). In SNOR, however, a nasal appliance is connected to any of several commonly-employed anesthesia circuits of tubing which are connected to anesthesia machines and/or other sources of oxygen, air and anesthetic gases. Gas flows can be used to generate the relatively low pressures through the nose that will usually relieve upper airway obstruction and allow spontaneous respiration.
Another common occurrence in the practice of anesthesia, in addition to SNOR, is the use of 100% oxygen or oxygen mixed with nitrous oxide. Nitrous oxide, itself, supports combustion and any combination of the two gases, when allowed onto the surgical field, will find plenty of fuel (e.g., plastic and paper drapes, hair, etc.) and ready sources of ignition (e.g., electro-cautery, LASER, fiberoptic lights, etc.). This potential joining of the three sides of the “fire triangle” can result in a chain reaction that is often explosive in its evolution and is the cause of, “. . . approximately 100 surgical fires each year, resulting in up to 20 serious injuries and one or two patient deaths annually.” (SENTINEL EVENT ALERT, Jun. 24, 2003, from the Joint Commission on Accreditation of Healthcare Organizations)
Other problems are associated with the use of high concentrations of oxygen and nitrous oxide. High oxygen concentrations over many hours can induce severe inflammation of the lungs and respiratory distress. Further, without nitrogen to keep them inflated, 100% oxygen is rapidly absorbed from under-ventilated alveoli, allowing them to collapse causing “absorption hypoxia” and a predisposition to pneumonia. Still further, nitrous oxide diffuses so rapidly from the circulation into the alveoli at the end of anesthesia that adequate oxygen can be prevented from entering the alveoli.
The solution to the above problems is as simple as eliminating nitrous oxide, the use of which is more traditional than helpful, and adding air to all anesthetic gases. The nitrogen in air dilutes the oxygen and absorbs heat to impede the chain reaction of combustion. The real problem is that many anesthesia settings do not have the capability to deliver air to the mixture of anesthesia gases. Operating rooms often have not been piped for air and many anesthesia machines are not designed to deliver air. Moreover, compressed “medical air” is expensive. Manual support of the airway such as with an invasive endotracheal tube, application of a face mask over the mouth and nose and various other airway devices are employed, often with supplemental oxygen.
However, the use of a face mask or an endotracheal tube during surgical procedures has many drawbacks. The standard face mask places pressure on the chin and tends to collapse soft-tissue structures of the oropharynx. Additionally, air pressure that is applied through the face mask tends to equalize through the nose and the mouth, and therefore it can be counter-productive to the supporting of soft tissue to open the airway. Further, using a face mask usually requires one or two additional maneuvers, for example manual support of the chin, the insertion of an oral airway, etc., in order to remedy the problem. None of the invasive airway-support devices currently used in conventional anesthesia practice can be inserted in the conscious patient without causing significant discomfort and/or physiological disturbance.
Furthermore, recent advances in cosmetic surgery have made airway management significantly more challenging and have caused practitioners to accept conditions having a reduced margin of safety for their patients. In particular, laser procedures on the face are requiring heavier sedation leading more often to respiratory depression and obstruction while, at the same time, the increased fire hazard restricts the use of oxygen.
Obstructive Sleep Apnea (OSA), a syndrome defined in the early 1980's, is similar to drug-induced obstructive apnea in anatomy and treatment. The treatment of OSA has demonstrated that upper airway obstruction occurring during the sleep of afflicted patients can be relieved by the application of positive pressure through the nose alone. OSA differs from drug-induced obstructive apnea in that it is not drug-induced. Further, OSA typically does not have acutely disastrous consequences, but rather has long-term ill-effects and is a chronic condition.
A conventional method for treating a form of OSA is to provide a continuous positive airway pressure (C-PAP) through the nose in order to prevent an upper airway obstruction. Nasal masks are used, as are nasal insert devices. InnoMed Technologies, for instance, provides a device called NasalAire used to treat obstructive sleep apnea. The device includes conical shaped nasal inserts connected to gas delivery tubes which are connected to an air delivery system. A C-PAP generator is included, which automatically increases and decreases air flow rate to maintain a continuos positive airway pressure. Furthermore, the device includes vent holes for venting CO2 from the exhaling user.
FIG. 1 illustrates a conventional system for treating sleep induced apnea by providing a constant positive airway pressure through the nose. As depicted in the figure, the patient 104 is fitted with tubing 102. The tubing 102 receives airflow from a C-PAP machine and administers the airflow to the nose of the patient by tube branches 106. An airflow delivery device 108, having nasal inserts 110 is placed such that nasal inserts 110 are disposed within the nasal vestibules 114 of patient 104. Airflow delivery device 108 additionally includes ventilation holes 112, which provide ventilation for CO2 from the user during expiration. Examples of such devices are disclosed in U.S. Pat. No. 5,533,506 to Wood, U.S. Pat. No. 4,702,832 to Tremble et al, and U.S. Pat. No. 5,134,995 to Gruenke et al., the entire disclosures of which are incorporated herein by reference.
What is needed is a method and apparatus for preventing complete airway obstruction of a patient when the patient is deeply sedated after induction of anesthesia.
What is additionally needed is a method and apparatus for enabling a patient to adequately respire at surgical levels of anesthesia without an invasive airway and manual or mechanized ventilation.
What is additionally needed is a method and apparatus for cost-effectively adding air to the anesthetic gasses for reducing the risk of combustion in the surgical field when using cautery or laser devices.
What is additionally needed is a method and apparatus for preventing leakage of the anesthesia to the operating room.
What is additionally needed is a method and apparatus for more accurately monitoring spontaneous respirations in a pressurized system.
What is additionally needed is a method and apparatus for preventing an airflow generator from excessively pressurizing an anesthesia circuit.
What is additionally needed is an apparatus that is: operably connectable to an existing anesthetic delivery apparatus; operable to prevent complete airway obstruction of a patient when the patient is deeply sedated after induction of anesthesia; and operable to enable a patient to adequately respire at surgical levels of anesthesia without an invasive airway and manual or mechanized ventilation.
What is additionally needed is an inexpensive method of adding air to the various breathing circuits used in the operating room, recovery room and other critical care areas. An airflow generator which does not store air in a compression tank, but immediately delivers it to the patient, could provide the same ambient air that the patient would be breathing on his own, if not being treated, and would draw from the same safe air supply breathed by those healthcare providers in attendance. Moreover, if a filter were attached to the airflow generator then the patient would, in theory, be breathing air more pure than ambient air.
As opposed to a conventional continuous-pressure airflow generator (i.e.,“C-PAP machine”), what is additionally needed is an airflow generator operable to generate a constant flow rate and allow the airway pressure to vary.
What is additionally needed, is a device (adapter) which could convert a standard “C-PAP Machine” from continuous-pressure air delivery to continuous-flow air delivery.
What is needed, is a reliable continuous breath-by-breath monitor of the breathing circuit and the patency of the upper airway of the patient. A stethoscope designed to fit in-line with the tubing of the breathing circuit would transmit the unique combined sounds of airflow through the circuit and upper airway of the patient. Such a stethoscope would give the earliest warning of impending airway obstruction and allow corrective action to be taken within a breath of discovery with immediate feedback as to the effectiveness of the remedy.
What is further needed is a simple and inexpensive mechanical monitor of inspiratory flow.
If the patient is intubated for general anesthesia, at the end of the surgical procedure, C-PAP may be applied as the patent is extubated relatively deep and unreactive to the endotracial tube. This allows the patient to awaken without the upper airway obstruction and the coughing and gagging that often accompanies emergence from endotracial anesthesia. In so doing, evasive airways are avoided, the functional residual capacity is optimize, atelectasis is prevented and elimination of the anesthetic vapors is promoted. Accordingly, what is needed is a way of continuously supplying C-PAP to a patient recovering from general anesthesia: from the time the anesthesia is turned off in the operating room, during transport to the recovery room; and through the entire recovery phase until the patient is well awake.